Xilinx Virtex-5 RocketIO GTP User Manual

Virtex-5 RocketIO GTP Transceiver User Guide www.xilinx.com 127
UG196 (v1.3) May 25, 2007
RX Termination and Equalization
R
The receiver includes four main features for optimizing signal integrity:
• Optional Built-In AC Coupling
• Configurable Termination Impedance
• Configurable Termination Voltage
• Optional Configurable RX Linear Equalization
Optional Built-In AC Coupling
The GTP receiver includes small AC-coupling capacitors that isolate the receiver from the
line. These capacitors are required when the RX termination is set to GND and are enabled
by default. When GND termination is not used, these capacitors can be disabled to allow
for DC coupling or more optimal off-chip AC coupling. See Chapter 10, “GTP-to-Board
Interface,” for more details about how to pick an appropriately sized external AC coupling
capacitor.
The AC_CAP_DIS attribute controls the AC-coupling bypass switch shown in Figure 7-2.
As required when built-in AC coupling is activated, RCV_TERM_MID activates the
2/3 MGTAVTTRX reference behind the built-in, AC-coupling circuit.
To turn on built-in AC coupling, AC_CAP_DIS is set to FALSE, and RCV_TERM_MID is
set to TRUE. To disable the built-in AC coupling, AC_CAP_DIS is set to TRUE, and
RCV_TERM_MID is set to FALSE.
Figure 7-2: Receiver Channel Internal Architecture
High-Pass Pole Location: RXEQPOLE[3:0]
Line Termination
MGTRXN
MGTRXP
Reference to 2/3 AVTTRX:
RCV_TERM_GND AND
RCV_TERM_VTTRX
Reference to Ground:
RCV_TERM_GND
Reference to AVTTRX:
RCV_TERM_VTTRX
AC Coupling Bypass:
AC_CAP_DIS
High-Pass/Wideband Mixing Ratio:
RXEQMIX[1:0]
RCV_TERM_MID
to
RX CDR
V1: 2/3 AVTTRX
V1: 2/3 AVTTRX
V2: AVTTRX
(1)
(1)
Single-Pole
High-Pass
Filter
_
+
+
++
V1
V1
V2
_
+
High Pass
Wideband
UG196_c7_02_030307
Notes:
1. The internal AC coupling capacitor is not a replacement for offchip coupling capacitors. It is an isolation capacitor for
nonstandard termination voltages.
2. These port names have the prefix MGT to identify them easily in a pad file that is very often used to create symbols for board
design schematics. In this document, the MGT prefix was removed from those names; however, names with and without the
MGT prefix are synonymous to each other.

Xilinx Virtex-5 RocketIO GTP Specifications

General

Brand	Xilinx
Model	Virtex-5 RocketIO GTP
Category	Transceiver
Language	English